PASSIVE UNDERGROUND ELECTRONIC MARKER FOR USE IN ANY ORIENTATION
A passive electronic marker comprising a single tuned LC circuit, having an inductance and one capacitance element, that respond substantially uniformly to a marker locating instrument irrespective of the orientation the marker was installed in. The inductance is split among more than one electrically contiguous coils; each of the coils is oriented in different axes along the three dimensional space to achieve the substantially uniform response to a marker locating instrument. The tuned circuit is enclosed in a protective housing that may or may not help in the orientation of the marker during burying. The passive marker is of a type that is buried relative to portions of an object for use in locating such objects when necessary.
Not Applicable
FEDERALLY SPONSORED RESEARCHNot Applicable
SEQUENCE LISTING OR PROGRAMNot Applicable
FIELD OF THE INVENTIONThe invention presented here relates to passive electronic markers of tuned capacitance-inductance type for use in locating buried objects by virtue of proximity to the marker buried alongside the object; more particularly to type of markers that can be buried without care to orientation of the marker installed.
BACKGROUND OF THE INVENTIONPrior art, U.S. Pat. No. 3,836,842, issued 1974, describes the passive marker as a tuned inductance-capacitance circuit, comprising a coil of conductive wire as inductance connected to a capacitor and tuned to the desired frequency. This assembly is encapsulated in non magnetic material for protection. Most modern passive markers and locators may be considered as variations of this prior art. The said prior art also describes a marker locating device. The marker locating device operates by transmitting an alternating magnetic field, this induces a current in the tuned passive marker circuit in proximity of the locating device. The locating device stops transmission and tries to receive, in the same axis as the transmitter, the magnetic field transmitted from the marker due to the current that resonate inside the passive marker before the current decays and thus detect the presence or absence of a passive marker. The said prior art also describes the detection profile with respect to marker depth. The maximum detection depth varies with soil and environmental conditions too. Prior art, U.S. Pat. No. 4,873,533, issued 1989, describes the typical turns in a coil that forms the inductance, typical capacitance value range, materials used, detection range and dimensions to give us an idea about these parameters.
Modern passive markers are mainly air cored markers that may be broadly divided into two types, a flat type and spherical type. Prior art, U.S. Pat. No. 4,334,227, issued 1982, describes a typical flat type of marker. This is a single frequency tuned Inductance-capacitance circuit with the coil in a flat plane and axis perpendicular to the plane of the coil. The problem with this type of marker is that the axis needs to be properly aligned with the marker locating devices transmitting and receiving antenna. This means that if the work site crew buries the flat marker without care to orientation, then detecting the marker becomes difficult or impossible depending on the size of the marker and the depth that it is at and the position of the marker coil axis. Underground movements of soil or differential settlement in a water logged site can also cause the marker to change orientation even after proper installation and may occur after many years making locating the marker difficult.
Prior art, U.S. Pat. No. 4,712,094, issued 1987, describes a spherical marker with a flat marker coil inside which aligns the coil axis in the direction of gravity. Thus this invention solves the problem of deliberate marker orientation requirement in the vertical direction by floating a flat marker in a liquid. The disadvantages with this arrangement are, added weight of the liquid, sealing requirements for heavy fluid, additional sealing requirement for the internal coil separate from outer shell, added cost of the materials and anti-freeze requirements for the liquid. Handling is consequently not smooth with liquid sloshing inside and added shipping cost. Additional sealing for coil and its need to move freely inside the marker means that the coil size is smaller relative to the marker further reducing the marker detection range. The marker does not provide maximum orientation free detection in directions other than vertical. For example, if installed on a slope above a flat area, this marker will be hard to detect walking along the flat area around the rising slope.
One way to get a true multidirectional response is, align flat markers in all three axes in one package. This kind of a solution is given in prior art, U.S. Pat. No. 5699048, issued 1997, which describes another spherical marker that overcomes the shortcomings with prior art, U.S. Pat. No. 4,712,094. It uses 2 or more isolated inductance-capacitance tuned circuits, each in a separate axis for improved multidirectional detectability. Diagram in
A single capacitance-inductance tuned circuit passive marker constructed in accordance with the present invention provides a true multidirectional response under all conditions, without a plurality of separate isolated tuned circuits, allowing orientation free marker. A passive marker constructed in accordance with the invention comprises two or more electrically contiguous coils oriented in three dimensional space such that the axes of the coils are at different positions or angles to each other; a capacitance, which together with the combined inductance of the coils, tune the circuit to a frequency; and a housing to enclose and insulate the said tuned circuit from the locating instrument as well as protect the said tuned circuit from common substances in the soil.
The other advantages of this invention are that there are no liquids and anti-freeze inside the marker, this marker is lighter than a liquid filled marker, the coils do not need a second enclosure to protect from liquid inside the marker, the coils in the marker can be as big as the enclosure depending on the coil arrangement and the response is mostly uniform in three dimensional space as opposed to a floated flat marker.
The additional advantages of this invention are that, each of the coils need not tuned individually, this results in lower number parts, joints and labor and consequently higher reliability, coils need not be wound, tuned and readied before assembly, continuous winding one coil after another is possible as the coils are not electrically isolated from one another.
The response from this invention is more uniform in all 3 dimensions as the same current flows in all 3 coils with axis oriented differently. This generates uniform magnetic field available for detection. This is true even when the transmitter and detector axes are at any angle to each other.
Markers that respond to two or more frequencies are possible by using a plurality of, single inductance-capacitance tuned multiaxis coil circuits, tuned to multiple frequencies. Markers that respond with higher response are possible by using a plurality of such single inductance-capacitance tuned multiaxis coil circuits tuned to the same frequency.
The invention described here provides a solution that allows a better orientation free passive marker.
Consider X-axis to be from the left to right of
The theory behind operation of a typical passive marker and marker locating device is briefly explained in the background of the invention. Assuming that the marker is buried fairly deep underground with orientation as in
Another embodiment of the invention may have coil bands 101, 102, 103 of
Another embodiment of the invention may have the enclosure halves 100, 104 with lips so that they can be joined by ultrasonic or heat welding. The enclosure halves may also have projections that allow the marker to be tied to an object.
Only a few embodiments that fall within the scope and spirit of the present invention have been described here.
Claims
1. A passive electronic marker for use in locating buried objects, comprising:
- a) a single capacitance-inductance tuned circuit.
- b) said inductance comprising two or more electrically contiguous coils oriented in three dimensional space such that the axes of said coils are at different positions or angles to each other.
- c) said capacitance, which together with the said inductance, tune the said circuit to one desired frequency.
- d) a housing to enclose and protect the said tuned circuit.
- e) said marker being buried without care of the orientation and being able to detect the said marker with a locating instrument more uniformly in any orientation.
2. A passive marker of claim 1 that can be located uniformly by a receiver in any axis when energized by a transmitter in any other axis.
3. A passive electronic marker for use in locating buried objects, comprising:
- a) a plurality of tuned circuits of claim 1, enclosed in a housing and buried.
Type: Application
Filed: Mar 5, 2010
Publication Date: Sep 8, 2011
Inventor: SAMEER CHOLAYIL (FORT WORTH, TX)
Application Number: 12/718,173
International Classification: G01V 3/08 (20060101);